Countercurrent chromatography (CCC) is a form of liquid-liquid partition chromatography which relies on continuous contact between two immiscible solvents, one of which is mobile relative to the other, in a flow-through tubular column, free of any solid support matrix. The retention time of a solute in the phase contact region of the system is determined by the volume ratio of the solvents, the partition coefficient of each solute between the solvents, and the degree of contact of the solvents with each other. Like other forms of liquid-liquid partition chromatography, one of the solvents serves as a carrier, drawing the solutes from the other at varying rates depending on the partition coefficients and carrying the solutes out of the column in the order of elution. This solvent can thus be referred to as the mobile phase, while the other solvent can be referred to as the stationary phase, event though it is not strictly stationary in many applications of the method. Solvent mixing in the column, retention of the stationary phase in the column, and solute partitioning in the column are all achieved with the aid of a suitable acceleration field established by gravity, centrifugal force or both, and the configuration of the column.
Most equipment used for CCC separations involves a coil of column tubing, a portion of which is filled with the stationary phase while the mobile phase is passed through it. By varying the length and diameter of the tubing, CCC has been used for both analytical and preparative separations. The flow rate of the mobile phase may be varied by varying the field imposed on the column. Units which operate with only a gravitational field imposed on the system are restricted to slow flow rates to avoid displacing the stationary phase, and the resulting separations typically require 1 to 3 days. By supplementing gravitational force with centrifugal force, one can achieve acceleration fields of 40 g or more, permitting faster flow rates which result in shorter separation times such as a few hours.
Countercurrent chromatography theory and apparatus are described in the literature. Examples of such disclosures are Ito Y., "Principle and Instrumentation of Countercurrent Chromatography," in Countercurrent Chromatography: Theory and Practice, Mandava, N.B. and Ito, Y., eds., pp. 79-442 (Marcel Dekker, New York, 1988); Conway, W.D., Countercurrent Chromatography: Apparatus, Theory and Applications (VCH, New York, 1990); and Shibusawa, Y., et al., U.S. Pat. No. 5,114,589, issued May 19, 1992.
Various types of rotation have been studied in attempts to vary the centrifugal force on the column. The optimal centrifugal force and the mode of rotation which gives rise to such a force will vary depending on the particular separation sought. One type of apparatus described in the literature for providing the centrifugal force is a cross-axis synchronous flow-through planet centrifuge, so called because of its ability to permit flow through a coiled column while rotating the column under two types of rotation at the same time--a rotation of the coiled column about its own axis, and a planetary rotation of the coiled column about an axis external to the coil. The present invention resides in an improvement in centrifuges of this type, permitting adjustment and variability of the placement of the coiled column on the centrifuge such that one can select a preferred mode of rotation for a particular separation.